Continuous chromatographic analysis



Oct. 10,1967 E. R. FENSKE CONTINUOUS CHROMATOGRAPHIC ANALYSIS 2Sheets-Sheet 1 Filed Jan. 28, 1964 Figure Measuring 0e Sample Out IReference Cell Sample In /v vf/v r05.- E llsworrh R. Fens/re oam 60sATTORNEYS United States Patent Ofiice 3,345,858 Patented Oct. 10, 19673,345,858 CONTINUOUS CHROMATOGRAPHIC ANALYSIS Ellsworth R. Fenske,Palatine, Ill., assignor to Universal Gil Products Company, Des Plaines,111., a corporation of Delaware Filed Jan. 28, 1964, Ser. No. 340,640 19Claims. (Cl. 73-23.1)

ABSTRACT OF THE DISCLOSURE Chromatographic analysis of a fluid mixtureutilizing as column packing a solid selective sorbent such as molecularsieves, incorporating a modified procedure which provides a continuousoutput signal, notwithstanding intermittent sample injection,proportional to concentration of selectively sorbed component(s) in saidmixture. The method is particularly adapted to determining totalnparafiin content of a mixture of normal and non-normal hydrocarbons.The column is first presaturated with nparaflins. Carrier gas is passedcontinually through the column, and fixed volume samples of the analysismixture are periodically injected into the carrier gas stream.Thereafter, the n-paraffin content is reflected by a continuous elevatedbaseline signal proportional to n-paraffin concentration, whichaccurately tracks changes in said concentration as between a pluralityof the series of samples. The non-normals of each sample are preferablyeluted as a single lumped peak superimposed upon the baseline signal.

This invention relates to a method for analyzing mixtures of fluidcomponents and more particularly to the analysis of such mixtures by animproved vapor phase chromatography technique utilizing as the componentseparating medium a solid sorbent capable of retaining one or morecomponents of the mixture and rejecting one or more other componentsthereof. More specifically the present invention is directed to a methodfor the rapid analysis of either or both of two broad classes ofcomponents present in a sample mixture: (1) those components which areselectively sorbed by the sorbent and (2) those components which arerelatively less sorbed or rejected by the sorbent. Those of the firstclass are analyzed continuously.

The theory and application of vapor phase chromatography is well known.Much of the work in this art has been directed to the development ofhigh resolution apparatus capable of separating and quantitativelymeasuring'very closely related compounds in a complex multicomponentsystem. Many sophisticated column designs have been developed which arecapable of handling sample, volumes in the microliter or even nanoliterrange; other designs'embody elaborate flow schemes, multiple columns,novel column packing materials, ultra-sensitive detectors, advancedelectronic circuitry, and the like, all with the objective of providingever higher resolution and sensitivity. For the most part suchcomplicated analytical equipment can be utilized to advantage only inthe laboratory by or under the supervision of a skilled technician.Equipment of this type has generally proven unsatisfactory, whentransferred to the chemical plant or petroleum refinery and utilized asa process stream analyzer, because it lacks reliability under adverseenvironment and needs considerable maintenance and calibration. Even thehighly engineered process stream chromatographs heretofore available foruse in field installations do not provide the complete answer and infact have at least four substantial drawbacks: first, conventionalchromatographs hav excessive capability, by which is meant they supply amore thorough analysis of a'multi-component stream than is needed by aplant operator who is usually interested in only one key component orgroup of components. Second, they require a relatively long time toelute a given sample, hence the interval between analyses is oftenunduly delayed which cannot be shortened even though the peaks not ofinterest are mechanically or electronically suppressed. Third, theoutput signal of a conventional chromatograph, being a train ofunidirectional peaks, is inherently discontinuous and therefore unsuitedto online process control unless it is taken through a peak-picker orintegrator and memory device,

' which auxiliary apparatus adds to system cost and reduces when donemanually, necessitates elaborate and expensive computing circuitry whendone electronically, and in any case the frequency of the determinationsremains limited by sample elution time.

The present invention largely eliminates the aforesaid disadvantages ofprior art chromatographic analyzers through the use of a speciallypretreated solid sorbent as the chromatographic column packing material.Various solid sorbents of specific composition and structure are knownwhich, upon contact with a mixture of components which differ in theirrelative sorbency on the solid, have the ability to selectively sorb oneor more components thereof and to pass or reject one or more othercomponents, thereby providing a means for segregating the individualcomponents according to their structure. The physical or chemicalmechanisms by which particular sorbents are operative for particularmulti-component mixtures may differ. For example, typical sorbentsoperative by reason of their adsorptive properties include silica gel,activated charcoal, aluminosilicates such as the various clays andactivated silica gels including, for example, Attapulgus clay,montmorillonite, dehydrated composites of alumina and silica activatedby heating to a temperature slightly below the fusion point of thecomposite, and activated alumnia; sorbents operative by molecularocclusion are the dehydrated metal aluminosilicate hydrates wherein themetal constituent is an alkali or alkaline earth metal, commonlyreferred to as molecular sieves. These and other types of sorbents, aswell as processes employing them, are well known in the art, and aremore completely described, for example, in US. Patent 2,985,589. Any ofthe above sorbents may be employed in the present invention.

In accordance with this invention there is provided a means for passinga continuous flow of carrier gas, such as helium, first through areference thermal conductivity cell, then successively through aseparating column and a measuring thermal conductivity cell. A sampleinjection means is provided for injecting controlled volume samples ofthe fluid mixture to be analyzed directly into the carrier gas streambetween the reference cell and the separating column. The reference celland measuring cell are incorporated in a suitable bridge circuit whichdrives a potentiometric recorder. These elements are conventional. Ihave discovered, however, that if the column is packed with a solidsorbent capable of selectively sorbing one or more, but less than all,of the components present in the sample, and further if the sorbent issubstantially presaturated with at least one of the selectively sorbedcomponents, then a true continuous analysis for the selectively sorbedmaterial can thereafter be obtained. The presaturation of the sorbentmay be effected by contacting it with the selectively sorbed componentor components, either in pure form or in admixture with relatively lesssorbed or non-sorbed components, under sorption conditions prior toloading it into the separating column; presaturation may also beaccomplished in situ, after the sorbent is loaded into the column, byrepetitive sample injection until substantial saturation is achieved.Consider first that the column is filled with fresh or only partiallysaturated sorbent, carrier gas flow is established at the proper rate,column temperature is stabilized at the proper level, and the measuringbridge circuit parameters are adjusted to provide an electrical zerooutput in the recorder. Assume that the fluid mixture to be analyzed isa binary mixture consisting of one selectively sorbed component and onerelatively less sorbed component. A first sample is injected and a shortwhile later a peak is recorded corresponding to passage of the lesssorbed component through the measuring cell; the recorder pen returns tozero and remains there since the selectively sorbed component originallypresent in the sample is captured by the sorbent and is not stripped ordesorbed by the carrier gas. The same response will be obtained aftereach of a number of successive sample injections until the sorbentbecomes saturated with respect to the selectively sorbed component. Whensaturation occurs the selectively sorbed component begins to elute at auniform rate from the separating column, even though another sample hasnot yet been injected, and the recorder pen will suddenly drive upscalea substantial distance above electrical zero corresponding to passage ofthe selectively sorbed component through the measuring cell. Thisresponse is not a peak but is a stable baseline elevated aboveelectrical zero which con tinues for a substantial period of timefollowing the last previous sample injection, and significantly themagnitude of such elevation has been found to be proportional to theamount by weight of selectively sorbed component present in the sample.If, now, successive samples of the fluid mixture are injectedperiodically, and the concentration of selectively sorbed component ineach is different, the analyzer output will have the form of a peak,soon after each Sample injection (due to the less sorbed component)superimposed on a continuous time-varying elevated baseline, the latteraccurately tracking the varying content of the selectively sorbedcomponent in the series of samples. The deflection above electrical zeroafter the less sorbed component peak provides a continuous measure ofthe selectively sorbed component content of the sampled binary system.The analyzer in effect converts a sampled data input to a continuousoutput.

Consider, next the case where the fluid mixture to be analyzed is amulti-component mixture consisting of two or more selectively sorbedcomponents and one relatively less sorbed component. After a number ofsample injections the sorbent becomes saturated with selectively sorbedmaterial which thereafter elutes at a uniform rate and withoutdiscrimination or chromatographic separation as among the severalselectively sorbed components. The analyzer output has the same form aswhen the fluid mixture is a binary system except that now the elevatedbaseline, after passage of the less sorbed component through theseparating column, is proportional to the total selectively sorbedcomponent content of the mixture. The analyzer in effect treats themulti component mixture as a pseudobinary system.

Consider further the case where the fluid mixture to be analyzedcomprises at least two selectively sorbed components and at least tworelatively less sorbed components. After the sorbent is saturated withselectively sorbed material, continued repetitive sample injectionresults in a continuous elevated baseline developed by the continuous,non-discriminatory elution of the several selectively sorbed components.If the temperature of the separating column is sufficiently low,chromatographic separation of the less sorbed components willnevertheless occur so that the analyzer output, following each sampleinjection, is a series of peaks, corresponding to the specificcomponents contained in the less sorbed class, deviating from theelevated baseline. While this type of analysis is frequently useful andis included within the scope of the invention, it is also desirable andpossible to make the analyzer respond as though the fluid mixture werebinary. This is accomplished by raising the column temperature to thepoint where all the less sorbed components are eluted from the columnalmost immediately and without discrimination, while the selectivelysorbed components continue to elute uniformly, also withoutdiscrimination, thereby achieving a lumping effect. The analyzer output,following each sample injection, now takes the form of a single narrowpeak or spike deviating above the elevated baseline, the latter beingproportional to the total selectively sorbed component content of thesample. When operated in this manner, e.g., to perform a pseudobinaryanalysis, the analyzer distinguishes only between two broad classes ofcomponents: those which are selectively sorbed, and those which arerelatively less sorbed. Such information is often invaluable to theplant operator who is seeking to optimize the performance of aparticular piece of hardware or refinery process unit, such as adistillation column or catcracker, and who is not interested in acompound-by-compound analysis of a stream. The pseudobinary analysis hasthe additional advantage that elution time per sample is generally at aminimum so that higher sampling frequencies may be used. The columntemperature necessary to achieve the lumping effect is dependent onseveral variables such as the type of sorbent, the specific compounds inthe mixture to be analyzed, the carrier gas flow rate, etc., but in anyevent can be ascertained by routine experimentation with a particularsystern.

It will be recognized that the method of this invention differs overprior art chromatographic analyzers in at least four important respects:

(1) At least one of the components of the analysis mixture is elutedfrom the column continuously, notwithstanding intermittent sampleinjection, and at least one other component is eluted discontinuously,in contrast to conventional chromatographs wherein each specificcomponent elutes discontinuously as a binary mixture with the carriergas.

(2) If the analysis mixture contains two or more selectively sorbedcomponents, these are eluted from th column continuously and Withoutdiscrimination. This technique deliberately provides for a zero ornegligible separation between the specific selectively sorbedcomponents, as opposed to the philosophy of the prior art which hassought to achieve high resolution between all specific components of theanalysis mixture.

(3) If the analysis mixture contains tWo or more less sorbed components,in a preferred embodiment of the invention these components are elutedsimultaneously or substantially so, within a very short time aftersample injection, and their time of passage through the measuring cellis short in comparison to the interval between sample injections.

(4) Elution time per sample is significantly less than that required byconventional chromatographs.

Advantages of the instant technique include the following: a continuousoutput signal is developed from a discontinuous input, attaining closertracking of a varying component concentration and easier marriage withstandard analog control elements to form a closed loop system; a singlecomponent or group of components develops a unitary signal proportionalto their weight concentration, which signal is continuous forselectively sorbed components and may be lumped into a single peak forless sorbed components, thereby eliminating the computing circuitryrequired for automatic component readout in high resolution work; therelatively short elution period permits a higher sampling frequency andtherefore increased accuracy and reduced dead time; the use of a solidsorbent as the chromatograph column packing material eliminates problemsof stability and substrate boilaway arising from conventional packingscomprising an inert solid carrier coated with a high-boiling organicliquid substrate.

It is, therefore, a broad embodiment of this invention to provide amethod for analyzing a mixture of fluid components, at least one ofwhich is selectively sorbed by contact with a solid sorbent (such as,for example, silica gel, activated charcoal, activated alumina, ormolecular sieves) and at least one other component is relatively lesssorbed by the sorbent, which comprises pretreating a mass of saidsorbent by contact with said selectively sorbed component until thesorbent is substantially saturated with respect to the selectivelysorbed component, passing a sample of said mixture together with acarrier gas stream through a separation zone containing the pretreatedsorbent, and passing the efiluent from said zone to a measuring cell.

A more specific embodiment of this invention is directed to a method foranalyzing a mixture of fluid compounds, at least one of which isselectively sorbed by contact with a solid sorbent and at least twoother compounds are relatively less sorbed by the sorbent, whichcomprises pretreating a mass of said sorbent by contact with theselectively sorbed compound until the sorbent is substantially saturatedwith respect to the selectively sorbed compound, passing a carrier gasstream through a separation zone containing the pretreated sorbent,introducing samples of said mixture at periodic intervals into thecarrier gas stream at a point upstreamfrom the separation zone,

the temperature of said zone being sufficiently high so that all of saidcompounds are maintained in the vapor phase therein and said less sorbedcompounds are eluted from the separation zone substantiallysimultaneously, and passing the effiuent from the separation zone to ameasuring cell.

A preferred solid sorbent is a material characterized as a dehydratedmetal aluminosilicate hydrate wherein the metal constituent is an alkalior alkaline earth metal, also known as molecular sieves. These sorbentsare particles having pore diameters in the range of 3 to 7 A. and arecapable of selectively sorbing a variety of compounds depending upon thespecific pore diameter range and size distribution. The molecular sievesmay be prepared by c0- precipiating or otherwise combining alumina,silica, and a metal oxide such as an oxide or hydroxide derivative of analkali metal such as sodium, lithium or potassium or of an alkalineearth metal, such as calcium, magnesium, barium or strontium to form auniform and intimately dispersed mixture of silica, alumina and themetal oxide or hydroxide, removing excess water from the mixed oxidesand thereafter heating the recovered dispersed mixture to a temperatureat which the water of hydration will be driven oif by evaporation fromthe particles. The resulting dehydrated mixed oxides are preferablycalcined at a temperature of from about 400 to 800 F. to improverigidity and strength of the particles. Methods for the preparation ofmolecular sieves are well documented in the literature, as set forth,for example, in U.S. Patents 2,882,244 and 2,882,243.

'One specific embodiment of the invention, using molecular sieves as thechromatographic column packing material, provides a method for analyzinga mixture of hydrocarbons containing at least one normal aliphatichydrocarbon and at least one non-normal hydrocarbon se- 6 lected fromthe group consisting of branched chain and cyclic hydrocarbons. Thenormal aliphatic hydrocarbon is selectively sorbed by the molecularsieves and, after saturation of the sieves therewith, elutescontinuously from the column. The non-normal hydrocarbon is passed bythe sieves and elutes as a band soon after sample injection. The normalaliphatic hydrocarbon may be saturated or unsaturated, e.g., a normalparaifin, or a straight chain olefin, diolefin or polyolefin, and maycontain from 1 to about 22 carbon atoms. The non-normal hydrocarbon maybe a branched chain parafiin, olefin, diolefin or polyolefin containingfrom 4 to about 22 carbon atoms, a cycloparaflln or cycloolefincontaining from 4 to about 22 carbon atoms, or a mononuclear orpolynuclear aromatic hydrocarbon containing from about 6 to about 22carbon atoms. Since the components undergoing chromatographic separationare in the vapor state, hydrocarbons containing more than 22 carbonatoms cannot generally be analyzed by this method because they are toodifiicultly vaporizable, even with the substantial reduction inhydrocarbon partial pressure afforded by excess amounts of carrier gas,and tend instead to thermally decompose and deposit coke upon the columnpacking. When the normal aliphatic hydrocarbon is a normal paraflin itmay therefore contain from 1 to 22 carbon atoms, and preferably is onecontaining from 4 to 18 carbon'atoms. The non-normal hydrocarbon maycontain from 4 to about 22 carbon atoms, and preferably is onecontaining from 4 to 18 carbon atoms. The lumping effect is most readilyachieved when the carbon number spread of the analysis mixture does notexceed about 6 to 8 carbon numbers.

This invention is especially well suited to analyzing kerosene fractionscomprising one or more normal paraffins containing from 10 to 16 carbonatoms, and one or more non-normal hydrocarbons containing from 6 to 16carbon atoms. For an analysis mixture of this type the temperature ofthe molecular sieve column should be at least 600 F. and preferablysomewhat higher, for example, in the range of 610650 F., in order toobtain continuous non-discriminatory elution of the normal parafiins, onthe one hand, and non-discriminatory lumped elution of the non-normalhydrocarbons on the other. Below about 600 F. some separation of the C-C fraction will begin. A typical analysis mixture may comprise a majorproportion of normal parafiins and a minor proportion of non-normalhydrocarbons, in which case the height or area under the peak due tonon-normals, superimposed on the continuous elevated baseline due tonormals, will provide a measure of the total non-normal content of thesample. Another typical analysis mixture may comprise a major proportionof non-normals and a minor proportion of normals, in which case thedisplacement above electrical zero after passage of the non-normal peakwill provide a continuous measure of the total normal parafiin contentof the sample.

Another specific embodiment of the invention, using molecular sieves asthe column packing material, provides a method for the continuousanalysis of water in a mixt-ure of water with one or more of thefollowing less sorbed materials: methane, ethane, propane, isobutane,hexane, oxygen, hydrogen, nitrogen, air and natural gas. The less sorbedmaterials are passed by the sieves and elute from the column as acompact band soon after sample injection. The water vapor is selectivelysorbed by the molecular sieves and, after saturation of the sievestherewith, elutes continuously to develop an elevated baseline signalthe height of which, after passage of the peak due to the less sorbedmaterials, is proportional to the water content of the sample.

Another specific embodiment of the invention, using molecular sieves asthe column packing material, provides a method for the continuousanalysis of hydrogen sulfide or mercaptans in a mixture of hydrogensulfide or mercaptans with one or more of the following less sorbedmaterials: methane, ethane, propane, normal butane, isobutane, normalpentane, isopentanes, normal hexane, normal heptane, normal octane,hydrogen, carbon dioxide, and natural gas. The less sorbed materials arepassed by the sieves and elute from the column as a compact band soonafter sample injection. The sulfur compounds are selectively sorbed bythe molecular sieves and, after saturation of the sieves therewith,elute continuously to develop an elevated baseline signal the height ofwhich, after passage of the peak due to less sorbed materials, isproportional to the sulfur compound content of the sample.

Another specific embodiment of the invention, using molecular sieves asthe column packing material, provides a method for the continuousanalysis of carbon dioxide in a mixture of carbon dioxide with one ormore of the following less sorbed materials: methane, ethane, ethylene,propane, butane, pentane, nitrogen, hydrogen and carbon monoxide. Theless sorbed materials are passed by the sieves and elute from the columnas a compact band soon after sample injection. The carbon dioxide isselectively sorbed by the molecular sieves and, after saturation of thesieves therewith, elutes continuously to produce an elevated baselinesignal the height of which, after passage of the peak due to the lesssorbed materials, is proportional to the carbon dioxide content of thesample.

Still another specific embodiment of the invention, using molecularsieves as the column packing material, provides a method for thecontinuous analysis of normal unsaturated C C aliphatic hydrocarbons ina mixture of one or more of such unsaturated hydrocarbons with one ormore of the following less sorbed materials: methane, ethane, oxygen,hydrogen and nitrogen. The less sorbed materials are passed by thesieves and elute from the column discontinuously soon after sampleinjection. The un saturated hydrocarbon is selectively sorbed by themolecular sieves and, after saturation of the sieves therewith, elutescontinuously to produce an elevated baseline signal the height of which,after passage of the peak due to the less sorbed materials, isproportional to the unsaturated aliphatic hydrocarbon content of thesample.

Still another specific embodiment of the invention, using molecularsieves as the column packing material, provides a method for thecontinuous analysis of isobutane in a mixture of isobutane with one ormore C -C parafiins. The C C par-afiins, being relatively less sorbed,are passed by the sieves and elute from the column as a compact bandsoon after sample injection. The isobutane is selectively sorbed by thesieves and, after saturation of the sieves therewith, elutescontinuously to produce an elevated baseline signal the height of which,after passage of the peak due to the less sorbed C C paraffins, isproportional to the isobutane content of the sample.

A still further specific embodiment of the invention, using molecularsieves as the column packing material, provides a method for thecontinuous analysis of mononuclear aromatic hydrocarbons in a mixture ofsuch mononuclear aromatic hydrocarbons with polynuclear aromatichydrocarbons. The polynuclear aromatics, being relatively less sorbed,are passed by the sieves and elute from the column as a compact bandsoon after sample injection. The mononuclear aromatics are selectivelysorbed by the molecular sieves and, after saturation of the sievestherewith, elute continuously to develop an elevated baseline signal theheight of which, after passage of the peak due to the polynucleararomatics, is proportional to the mononuclear aromatic content of thesample.

Yet another specific embodiment of the invention, using as the columnpacking material a solid adsorbent such as dehydrated silica gel,activated charcoal, activated alumina, etc., furnishes a method for thecontinuous determination of mercaptans or amines in a mixture ofmercaptans or amines with a parafiinic hydrocarbon fraction. Theparafiins, being relatively less adsorbed, are passed by the adsorbentand elute from the column as a compact band soon after sample injection.The polar mercaptans or amines are selectively adsorbed and, aftersaturation of the adsorbent therewith, elute continuously to develop anelevated baseline signal the height of which, after passage of the peakdue to the parafiins, is proportional to the mercaptan or amine contentof the sample.

Still another specific embodiment of the invention, using as the columnpacking material a solid adsorbent such as dehydrated silica gel,activated charcoal, activated alumina, etc., furnishes a method for thecontinuous determination of olefins in a mixture of olefins andparaffins. The parafiins, being relatively less adsorbed, are passed bythe adsorbent and elute from the column as a compact band soon aftersample injection. The olefins are selectively adsorbed and, aftersaturation of the adsorbent therewith, elute continuously to develop anelevated baseline signal the height of which, after passage of the peakdue to the paraflins, is proportional to the olefin content of thesample.

Still another specific embodiment of the invention, using as the columnpacking material a solid adsorbent such as dehydrated silica gel,activated charcoal, activated alumina, etc., provides a method for thecontinuous determination of aromatic hydrocarbons in a mixture ofaromatic hydrocarbons and non-aromatic hydrocarbons. The non-aromatics,being relatively less adsorbed, are passed by the adsorbent and el-utefrom the column as a compact band soon after sample injection. Thearomatics are selectively adsorbed and, after saturation of theadsorbent therewith, elute continuously to develop an elevated baselinesignal the height of which, after passage of the peak due to thenon-aromatic hydrocarbons, is proportional to the aromatic hydrocarboncontent of the sample.

In still another embodiment of the invention, employing as the columnpacking material a solid adsorbent such as dehydrated silica gel,activated charcoal, activated alumina, etc., there is provided a methodfor the continuous determination of water vapor in a mixture of watervapor with air, nitrogen or other inert gas, or paraffinic hydrocarbons.The air, nitrogen, inert gas or parafiinic hydrocarbons, as the case maybe, being relatively less adsorbed, are passed by the adsorbent andelute from the column as a compact band soon after sample injection. Thewater vapor is selectively adsorbed and, after saturation of theadsorbent therewith, elutes continuously to develop an elevated baselinesignal the height of which, after passage of the peak due to the lessadsorbed materials, is proportional to the water vapor content of thesample.

The invention is specifically described in connection with theaccompanying drawings of which:

FIGURE 1 is a schematic diagram of a process stream analyzer embodyingthe invention.

FIGURE 2 is a schematic diagram of a bridge circuit for deriving anoutput signal from the apparatus of FIGURE 1.

FIGURE 3 is a plot of a typical output signal developed by the method ofthis invention.

With reference to FIGURE 1, there is shown in partial section a linearsample valve 10 which comprises outer stator plates 11 and an innerreciprocable plug 16 in fluid-tight contact with plates 11. Stator 11 isprovided with ports 12, 13, 14 and 15. Plug 16- is provided with threetransverse ports 17, 18 and 19; intermediate port 18 is of somewhatsmaller diameter and is the sample or metering port. Plug 16 is drivento either of its two adjusted positions by means of a shaft 20 which isconnected to an upper diaphragm operator 21 and also to a lowerdiaphragm operator 23. Actuating air is alternately supplied (throughsuitable automatically programmed valving, not shown) through line 22 tooperator 21 or through line 24 to operator 23; when one of lines 22 and24 is under pressure, the other line is simultaneously vented. Withoperator 23 pressured, plug 16 is moved upwardly into the position shownwhich is the sample port refill position: ports 12, 18 and 13 are inserial fluid communication, ports 14, 19 and 15 are in serial fluidcommunication, and port 17 is inoperative. With operator 21 pressured,plug 16 is moved downwardly into the sample injection position: ports12, 17 and 13 are now in serial fluid communication, ports 14, 18 and 15are in series fluid communication and port 19 is inoperative. Samplevalve 10 is enclosed by an electrically heated, temperature controlledjacket 25 which maintains the valve at an elevated temperaturesuflicient to preheat, partially vaporize or completely vaporize thesample, as desired. A circulating sample stream of the process fluid tobe analyzed is introduced through inlet line 26, filter 27 and line28 tovalve 10; it passes through either port 18 or port 17 and is Withdrawnthrough line 29, flow controller 30 and line 31, from which it mayconveniently be returned to a point in the process under lower pressurethan the inlet. The volume and length of tubing runs of the sample loopshould be kept as small as practicable to minimize transport lag. Asource of carrier gas 32 is connected to the analyzer by line 33. Thecarrier gas is preferably helium, but may also be neon, argon, hydrogen,nitrogen, C or other inert gas differing substantially in thermalcharacteristics from the components of interest in the sample stream.From line 33 the carrier gas is taken through a flow controller 34, line35, reference thermal conductivity cell 36 and line 37 to valve itpasses through either port 18 or port 19 and then through line 38 toseparating solumn 39 which contains a suitable solid sorbent. Vaporeflluent from column 39 flows through a measuring thermal conductivitycell 40 and is then vented through line 41. It will be appreciated thatother types of detection devices may be substituted for the thermalconductivity cell, for example, this may be an ionization detector or abeta ray detector. Cells 36 and 40 and column 39 are encased in anelectrically heated, temperature controlled detector block 42 whichholds the column at a temperature sufliciently high to vaporize all ofthe components in the sample and, where the sample mixture contains morethan one selectively sorbed component or more than one less sorbedcomponent, sufliciently high to prevent any appreciable separation asbetween the selectively sorbed components and, preferably, also asbetween the less sorbed components. The sample valve, detector block andcarrier gas flow controller are mounted in a temperature controlledhousing 43 adapted to provide an interior temperature in the range of60-120 F.

When valve 10 is inthe sample port refill position, process fluidentering lines 26 and 28 flows through port 18 and is returned throughlines 29 and 31 to the process or to a suitable sump or drain. Carriergas is admitted through lines 33 and 35 to reference cell 36, passesthrough port 19, line 38, column 39, measuring cell 40, and vent line41. When valve 10 is in the sample injection position, plug port 18 ismoved down to register with stator ports 14 and and the sample trappedtherein is swept out by the carrier gas into column 39 and thence tomeasuring cell 40. Plug port 17 moves down into registry with statorports 12 and 13 to provide continuity of sample loop flow during thesample injection portion of the operating cycle. Frequency of sampleinjection may be varied from as much as 10 times per minute to onceevery ten mniutes depending on the mixture to be analyzed, type ofsorbent, length of column, column temperature, etc. The response time ofthe analyzer itself can frequently be made less than about five secondsafter the sample is injected. One sample injection every one-two minutesis usually quite adequate for process monitoring and controlapplications and is preferred to allow time for operation of auxiliaryapparatus such as a peak picker or bridge zeroing servo. Notwithstandingthe intermittent nature of sample injections, a continuous output signalwith respect to the selectively sorbed component or components isreadily obtained.

In FIGURE 2 there is illustrated a suitable two-element bridge circuit50 for obtaining an output signal. One side of the bridge contains afixed resistor 51 connected in series with a temperature sensitiveresistive filament 56 within reference cell 36. The other side of thebridge contains the series combination of potentiometer 52 (coarse zeroadjustment), fixed resistor 53, potentiometer 54 (fine zero adjustment)and a temperaure sensitive resistive filament 55 within measuring cell40. Both sides of bridge 50 are connected through a voltage divider 57(attenuation adjustment) across which is connected a potentiometricrecorder 58. A constant current source 59 supplies regulated current tobridge 50 through a milliammeter 60. Obviously there are many otherfunctionally equivalent circuits which could be used; for example, afour-element bridge would increase the sensitivity two-fold.

As an example of the operation and response of the invention, apparatusof the above-described construction may be employed to analyze ahydrocarbon stream consisting of about 60i5% by weight of C -C normalparaflins and about 40i5% by weight of C -C nonnormal hydrocarbons(branched chain alkanes, aromatics and naphthenes). The separatingcolumn is 5 inches in length x A inch in diameterand contains about 1.9grams of molecular sieves (a dehydrated calcium aluminosilicate hydratehaving a pore diameter of about 5 A.). The volume of the sampleinjection port of the liner sample valve is 3 microliters. Operatingconditions are established as follows:

Sample valve temperature 320-330 F. Detector block temperature 625 6'35F.

The response of the analyzer is shown in FIGURE 3 in which the recorderoutput is plotted as a function of time. The abscissa representselectrical zero, which is determined by the measuring bridge circuitparameters and may or may not coincide with chart zero. The arrowsmarked I indicate successive sample injections. During the initialportion of this run, embracing peaks 61 and 62, each of which correspondto the total non-normal hydrocarbons lumped together, the molecularsieve sorbent is not as yet substantially saturated with normalparafiins, and the normals are therefore occluded by the sorbent and donot emerge from the column. The recorder pen returns to the electricalzero baseline after each of nonnormal peaks 61 and 62 has passed. Atpoint 11, however, the sorbent has finally become saturated with thenormal paraflins, which commence to elute continuously thereafter, andthe analyzer output increases rapidly. Peaks 63 and 65 each representthe total non-normal hydrocarbon content of the respective sample, butthey are now superimposed on an elevated baseline 64. In other words,even though the sample injections occur at rather wide intervals of 60seconds, the recorder pen does not return to zero but draws asubstantially continuous stable line 64, except for the intermittentnon-normal peaks. The height of line 64 above electrical zero isproportional to the total normal paraffin content by weight of thesampled stream and, surprisingly, follows small variations of the normalhydrocarbon content of successive samples with high accuracy. Thenon-normal hydrocarbons elute almost immediately without discriminationand all the normal parafiins elute continuously, also withoutdiscrimination.

Mixtures other than hydrocarbons, such as those set forth above, may beanalyzed in similar fashion. In all cases a continuous output signalcorresponding to the selectively sorbed material is obtained byutilizing a solid sorbent which has been substantially saturated withrespect to the selectively sorbed material. Where the analysis mixturecomprises more than one selectively sorbed component, the temperature ofthe separating column is sufficiently elevated so that little or noseparation of the selectively sorbed component will occur. And in apreferred embodiment of the invention, when the analysis mixturecomprises more than one less sorbed component, the temperature of theseparating column is held sufficiently high so that no significantseparation of the less sorbed components will occur and these aretherefore lumped together in a single peak which elutes soon aftersample injection. In this manner a unitary signal is developed which isproportional to the weight concentration of a single component or agroup of components which is selectively sorbed by the solid sorbent andthere is also developed a unitary peak corresponding to the weightconcentration of all the less sorbed components. The elution time persample is markedly reduced over that provided by conventionalchromatographic analyzers, therefore permitting a higher samplingfrequency, increased accuracy and reduced dead time. The invention alsopermits a very high order of accuracy and sensitivity with respect tothe selectively sorbed material, because by using larger sample volumesand/or more frequent sample injections, the effective concentration ofsorbed material in the separating zone effluent may be multiplied manyfold, whereby concentrations of the order of 15 p.p.m. Will produce adetectable output signal without the need for ultrahigh signalamplification.

I claim as my invention:

1. A method for analyzing a mixture of fluid components at least one ofwhich is selectively sorbed by contact with a solid sorbent and at leastone other component is relatively less sorbed by the sorbent, whichcomprises pretreating a mass of said sorbent by contact with saidselectively sorbed component until the sorbent is substantiallysaturated with respect to the selectively sorbed component, passing acarrier gas stream through a separation zone containing the pretreatingsorbent, introducing fixed volume samples of said mixture at periodicintervals into the carrier gas stream at a point upstream from theseparation zone, passing the effluent from said zone to a measuringcell, and developing from said cell a substantially continuous elevatedbaseline signal, the magnitude of which is proportional to theconcentration of selectively sorbed component in said sampled mixtureand which responds to changes in said concentration as between aplurality of the resulting series of samples.

2. The method of claim 1 wherein said sorbent is silica gel.

3. The method of claim 1 wherein said sorbent is activated charcoal.

4. The method of claim 1 wherein said sorbent is activated alumina.

5. The method of claim 1 wherein said sorbent is a dehydrated metalaluminosilicate hydrate.

6. A method for analyzing a mixture of fluid compounds, at least one ofwhich is selectively sorbed by contact with a solid sorbent consistingof a dehydrated metal aluminosilicate hydrate and at least one othercompound is relatively less sorbed by the sorbent, which comprisespretreating a mass of said sorbent by contact with said selectivelysorbed compound until the sorbent is substantially saturated withrespect to the selectively sorbed compound, passing a carrier gas streamthrough a separation zone containing the pretreated sorbent, introducingfixed volume samples of said mixture at periodic intervals into thecarrier gas stream at a point upstream from the separation zone, passingthe effluent from said zone to a measuring cell, and developing fromsaid cell a substantially continuous elevated baseline signal, themagnitude of which is proportional to the concentration of selectivelysorbed compound in said sampled mixture and which responds to changes insaid concentration as between a plurality of the resulting series ofsamples.

7. A method for analyzing a mixture of fluid hydrocarbons, at least oneof which is selectively sorbed by contact with a solid sorbentconsisting of a dehydrated metal aluminosilicate hydrate and at leastone other hydrocarbon is relatively less sorbed by the sorbent, whichcomprises pretreating a mass of said sorbent by contact with saidselectively sorbed hydrocarbon until the sorbent is substantiallysaturated with respect to the selectively sorbed hydrocarbon, passing acarrier gas stream through a separation Zone containing the pretreatedsorbent, introducing fixed volume samples of said mixture at periodicintervals into the carrier gas stream at a point upstream from theseparation zone, passing the efliuent from said zone to a measuringcell, and developing from said cell a substantially continuous elevatedbaseline signal, the magnitude of which is proportional to theconcentration of selectively sorbed hydrocarbon in said sampled mixtureand which responds to changes in said concentration as between aplurality of the resulting series of samples.

8. The method of claim 7 wherein said selectively sorbed hydrocarbon isa normal aliphatic hydrocarbon and said less sorbed hydrocarbon is anon-normal hydrocarbon selected from the group consisting of branchedchain and cyclic hydrocarbons.

9. The method of claim 7 wherein said selectively sorbed hydrocarbon isa normal paraflin and said less sorbed hydrocarbon is a non-normalhydrocarbon selected from the group consisting of branched chain andcyclic hydrocarbons.

10. The method of claim 9 wherein said normal paraffin contains from 1to 22 carbon atoms and said nonnormal hydrocarbon contains from 4 to 22carbon atoms.

11. The method of claim 9 wherein said normal paraffin contains from 4to 18 carbon atoms and said nonnormal hydrocarbon contains from 4 to 18carbon atoms.

12. The method of claim 9 wherein said normal paraffin contains from 10to 16 carbon atoms and said nonnormal hydrocarbon contains from 6 to 16carbon atoms.

13. A method for analyzing a mixture of fluid compounds, at least one ofwhich is selectively sorbed by contact with a solid sorbent and at leasttwo other compounds are relatively less sorbed by the sorbent, whichcomprises pretreating a mass of said sorbent by contact with saidselectively sorbed compound until the sorbent is substantially saturatedwith respect to the selectively sorbed compound, passing a carrier gasstream through a separation zone containing the pretreated sorbent,introducing fixed volume samples of said mixture at periodic intervalsinto the carrier gas stream at a point upstream from the separationzone, the temperature of said zone being sufliciently high so that allof said compounds are maintained in the vapor phase therein and saidless sorbed compounds are eluted from the separation zone substantiallysimultaneously, passing the effluent from said zone to a measuring cell,and developing from said cell a substantially continuous elevatedbaseline signal, the magnitude of which is proportional to theconcentration of selectively sorbed compound in said sampled mixture andwhich responds to changes in said concentration as between a pluralityof the resulting series of samples, and said baseline signal havingsuperimposed thereon a single peak for each of said samplescorresponding to the total less sorbed compounds contained in suchsample.

14. A method for analyzing a mixture of fluid hydrocarbons, at least oneof which is selectively sorbed by contact with a solid sorbentconsisting of a dehydrated metal aluminosilicate hydrate and at leasttwo other hydrocarbons are relatively less sorbed by the sorbent, whichcomprises pretreating a mass of said sorbent by contact with saidselectively sorbed hydrocarbon until the sorbent is substantiallysaturated with respect to the selectively sorbed hydrocarbon, passing acarrier gas stream through a separation zone containing the pretreatedsorbent, introducing fixed volume samples of said mixture at periodicintervals into the carrier gas stream at a point upstream from theseparation zone, the temperature of said zone being sufiiciently high sothat all of said hydrocarbons are maintained in the vapor phase thereinand said less sorbed hydrocarbons are eluted from the separation zonesubstantially simultaneously, passing the effluent from said zone to ameasuring cell, and developing from said cell a substantially continuouselevated baseline signal, the magnitude of which is proportional to theconcentration of selectively sorbed hydrocarbon in said sampled mixtureand which responds to changes in said concentration as between aplurality of the resulting series of samples, and said baseline signalhaving superimposed thereon a single peak for each of said samplescorresponding to the total less sorbed hydrocarbons contained in suchsample.

15. The method of claim 14 wherein said selectively sorbed hydrocarbonis a normal aliphatic hydrocarbon and said less sorbed hydrocarbons arenon-normal hydrocarbons selected from the group consisting of branchedchain and cyclic hydrocarbons.

16. The method of claim 14 wherein said selectively sorbed hydrocarbonis a normal paraffin and said less sorbed hydrocarbons are non-normalhydrocarbons selected from the group consisting of branched chain andcyclic hydrocarbons.

17. A method for the continuous chromatographic analysis of the totalaliphatic hydrocarbon content of a mixture of fluid hydrocarbonscontaining from 4 to 18 carbon atoms, at least one of which is a normalaliphatic hydrocarbon selectively sorbed by contact with a solid sorbentconsisting of a dehydrated metal aluminosilicate hydrate and at leasttwo other hydrocarbons are non-normal hydrocarbons selected from thegroup consisting of branched chain and cyclic hydrocarbons which arerelatively less sorbed by the sorbent, which method comprisespretreating a mass of said sorbent by contact with said normal aliphatichydrocarbon until the sorbent is substantially saturated with respect tothe normal aliphatic hydrocarbon, passing a carrier gas stream through aseparation zone containing the pretreated sorbent, introducing fixedvolume samples of said mixture at periodic intervals into the carriergas stream at a point upstream from the separation zone, the temperatureof said zone being sufli-ciently high so that all of said hydrocarbonsare maintained in the vapor phase therein and said nonnormalhydrocarbons are eluted from the separation zone substantiallysimultaneously, passing the effluent from said zone to a measuring cell,and developing from said cell "a substantially continuous elevatedbaseline signal, the

magnitude of which is proportional to the concentration of selectivelysorbed normal aliphatic hydrocarbon in said sampled mixture and whichresponds to changes in said concentration as between a plurality of theresulting series of samples, and said baseline signal havingsuperimposed thereon a single peak for each of said samplescorresponding to the total non-normal hydrocarbons contained in suchsample.

18. A method for the continuous chromatographic analysis of the totalnormal paraflin content of a mixture of fluid hydrocarbons, at least oneof which is a normal paraflin containing from 10 to 16 carbon atoms andwhich is selectively sorbed by contact with a solid sorbent consistingof a dehydrated metal aluminosilicate hydrate and at least two otherhydrocarbons are non-normal hydrocarbons seleoted from the groupconsisting of branched chain and cyclic hydrocarbons containing from 6to 16 carbon atoms and which are relatively less sorbed by the sorbent,which method comprises pretreating a mass of said sorbent by contactwith said normal parafiin until the sorbent is substantially saturatedwith respect to the normal paraffin, passing a carrier gas streamthrough a separation zone containing the pretreated sorbent, introducingfixed volume samples of said mixture at periodic intervals into thecarrier gas stream at a point upstream from the separation zone, thetemperature of said zone being sufiiciently high so that all of saidhydrocarbons are maintained in the vapor phase therein and saidnon-normal hydrocarbons are eluted from the separation zonesubstantially simultaneously, passing the efiluent from said zone to ameasuring cell, and developing from said cell a substantially continuouselevated baseline signal, the magnitude of which is proportional to theconcentration of selectively sorbed normal parafiin in said sampledmixture and which responds to changes in said concentration as between aplurality of the resulting series of samples, and said baseline signalhaving superimposed thereon a single peak for each of said samplescorresponding to the total non-normal hydrocarbons contained in suchsample.

19. The method of claim 18 wherein the temperature of the separationzone is above about 600 F.

References Cited UNITED STATES PATENTS 5/1961 Boeke 73-23.1

JAMES J. GILL, Acting Primary Examiner. RICHARD C. QUIESSER, Examiner,

1. A METHOD FOR ANALYZING A MIXTURE OF FLUID COMPONENTS AT LEAST ONE OFWHICH IS SELECTIVELY SORBED BY CONTACT WITH A SOLID SORBENT AND AT LEASTONE OTHER COMPONENT IS RELATIVELY LESS SORBED BY THE SORBENT, WHICHCOMPRISES PRETREATING A MASS OF SAID SORBENT BY CONTACT WITH SAIDSELECTIVELY SORBED COMPONENT UNTIL THE SORBENT IS SUBSTANTIALLYSATURATED WITH RESPECT TO THE SELECTIVELY SORBED COMPONENT, PASSING ACARRIER GAS STREAM THROUGH A SEPARATION ZONE CONTAINING THE PRETREATINGSORBENT, INTRODUCING FIXED VOLUME SAMPLES OF SAID MIXTURE AT PERIODICINTERVALS INTO THE CARRIER GAS STREAM AT A POINT UPSTREAM FROM THESEPARATION ZONE, PASSING THE EFFLUENT FROM SAID ZONE TO A MEASURINGCELL, AND DEVELOPING FROM SAID CELL A SUBSTANTIALLY CONTINUOUS ELEVATEDBASELINE SIGNAL, THE MAGNITUDE OF WHICH IS PROPORTIONAL TO THECONCENTRATION OF SELECTIVELY SORBED COMPONENT IN SAID SAMPLED MIXTUREAND WHICH RESPONDS TO CHANGES IN SAID CONCENTRATION AS BETWEEN APLURALITY OF THE RESULTING SERIES OF SAMPLES.